Amphibian collapses increase malaria outbreaks

The Amphibian Chytrid Fungus (Batrachochytrium dendrobatidis) is a highly contagious fungus that infects the skin of amphibians, blocking them from breathing and is eventually fatal. Ponds hit by the fungus are quickly choked by dead or almost dead frogs. It is so deadly and so easily spread that it has already caused the extinction of an estimated 90 species of frogs, and reduced the populations of another 124 species by over 90%. This makes it “the most destructive pathogen ever described by science,” as Wendy Palen, biologist, wrote in an article last year. One study traced its origin to Korea in the 1950s, after which humans spread it across the world.

[Image: Geoff Gallice]

Frogs and other amphibians consume a large amount of mosquitoes. If you remove a huge number of these amphibians from their habitat, you can image what must happen to malaria rates.

Researchers cross-referenced dates of Amphibian Chytrid Fungus-driven amphibian decline in different parts of Costa Rica and Panama with changes in malaria incidence in those same places[1]. The Amphibian Chytrid Fungus swept across these two countries over the course of about twenty-five years, starting in north-western Costa Rica and then slowly, but surely progressing south and east. They found that, generally, around a year after the Amphibian Chytrid Fungus entered a county, malaria cases began to increase. They continue to rise for two years, then stay at that higher level for six more, before beginning to attenuate nine years after the fungus arrived.

“For the six years our estimated effect of amphibian decline is at its highest, the annual expected increase in malaria ranges from 0.76-1.0 additional cases per 1,000 population,” they write, which makes up “a substantial share of cases overall.” This rate of increase in Costa Rica’s capital, San Jose, would translate to 1000 more cases there.

While it’s possible that something besides a causal relationship could explain these numbers, it is “extremely unlikely,” the authors write.

“The results in our paper suggest that some policies, such as amphibian conservation policies or the regulation of wildlife trade, could have benefits for human health which are not currently accounted for,” fellow-author Joakim Weill, says.

Whatever happens, Mother Nature has already found another way of killing amphibians, because a recently described second species, Batrachochytrium salamandrivorans, also cause chytridiomycosis and death in salamanders and newts in The Netherlands[2].

[1] Springborn et al: Amphibian collapses exacerbated malaria outbreaks in Central America in MedrΧiv - 2020
[2] Martel et al: Batrachochytrium salamandrivorans sp. nov. causes lethal chytridiomycosis in amphibians in PNAS - 2013